import React, { memo, useState, useMemo } from 'react'

const App = memo(() => {
  const [count, setCount] = useState(0)
  const doubleCount = useMemo(() => count * 2, [count])
  return (
    <div>
      <div>hello App</div>
      <div>{doubleCount}</div>
      <button onClick={e => setCount(count++)}></button>
    </div>


  )
})

export default App